1. Field of the Invention
The present invention relates to a battery pack system for a secondary battery with a positive electrode containing a nickel oxide as an active material, such as a nickel-metal hydride (Ni-MH) secondary battery. In particular, the present invention relates to a battery pack system applicable to appliances that are charged by a voltage control as in a lead storage battery or the like.
2. Description of Related Art
The following is a description of a conventional battery pack system, with reference to FIG. 4.
FIG. 4 shows a schematic configuration of a conventional battery pack system. In FIG. 4, a conventional battery pack system 40 includes a positive electrode terminal 41 and a negative electrode terminal 42, which are input/output terminals to be connected to the side of an appliance using this system, a battery 43 including at least one unit cell serving as a secondary battery, a detecting portion 44 for detecting a battery state BS (for example, voltage, current, temperature or a charging state) of the battery 43, and a controlling terminal 45, connected to the appliance side, to which information BI regarding the battery state is outputted from the detecting portion 44.
In this battery pack system 40, information BI regarding the battery state usually is transmitted from the detecting portion 44 via the controlling terminal 45 to the side of an appliance using this battery pack system 40. The appliance using this system is configured to control charging/discharging of the battery pack system 40 based on the received information BI regarding the battery state (for example, charging state information).
In order to achieve higher performance and lighter weight of an appliance using this battery pack system 40, it is desirable for a user that this battery pack system 40 can be replaced easily with that including a light-weight, high output-performance and long-life secondary battery without any modification in the configuration of a charging device on the appliance side.
For example, JP 9(1997)-285018 A discloses a battery pack system including a lithium-ion secondary battery that is charged by a voltage control. This battery pack system is compatible with a battery pack including a nickel-cadmium secondary battery, which is charged by a current control, also at the time of charging and has a higher energy density than the nickel-cadmium secondary battery (in other words, can accumulate energy more densely).
When using this battery pack system, there is an advantage in that the battery pack can be replaced without modifying the configuration of a charging device on the side of the appliance using the battery pack including the nickel-cadmium secondary battery.
However, in some cases the appliance using the battery pack system is configured to control charging by the voltage control, whose configuration is simpler than that of the current control, for the purpose of using lead storage batteries and lithium-ion secondary batteries. When attempting to mount a battery pack system including a nickel-metal hydride secondary battery with high performance that has both a high energy density and a high output density on such an appliance, since the appliance side has to control charging based on the information regarding the battery state transmitted from the detecting portion, an extensive modification of the charging device becomes necessary, leading to a cost increase.